function hideWarning(){
    var warningElement=document.getElementById("warning");
    warningElement.style.display="none";
}
var id;
function returnTop(){
id=setInterval('goTop()',10);

}
function goTop(){
scrollBy(0,-10);
    var scrollTop=document.documentElement.scrollTop+document.body.scrollTop;
    if(scrollTop==0){
        clearInterval(id);
    }

}
window.onscroll=function(){
    var scrollTop=document.documentElement.scrollTop+document.body.scrollTop;
    var topbar=document.getElementById('top-bar');
    var placeholderDiv=document.getElementById('placeholder-div');
    if(scrollTop>150){
        topbar.style.display='block';
        placeholderDiv.style.display='block';
    }else{
        topbar.style.display='none';
        placeholderDiv.style.display='none';
    }
}